Assessment of N-efficiency and N-responsiveness of Six Wheat (Triticum aestivum L.) Genotypes and their F1 and F2 Diallel Crosses

Screening wheat germplasm based on grain yield (GYPP) and nitrogen use efficiency (NUE) under contrasting N environments may be useful in identifying N-efficient (low-N tolerant) and responsive genotypes of great value in breeding programs. The main aim of the present study was to assess six wheat parents and their F1 and F2 diallel crosses for tolerance to low-N (N-efficiency) and responsiveness to high-N. A split plot design in a lattice arrangement with three replications was used in two-season experiment. Combined analysis across seasons indicated that mean squares due to genotypes (G), nitrogen levels (N) and G x N interaction were significant for most studied traits. In general, means of most studied traits of the three parents L25 , L26 and L27 were higher in magnitude than those of the three other parents Gem 7, Gem 9 and Giza 168 under both high-N and low-N levels. The highest mean of GYPP under low-N was obtained from L26 × L27 followed by L25 × L26 and L25 × L27 in F1 and L25 × L27 followed by L25 × L26 and L26 × Gz 168 in F2 generation. Superiority of low-N tolerant (T) over sensitive (S) parents, F1's and F2's in GYPP (40.54%) under low-N was 40.54, 40.42 and 40.62%, respectively. Superiority in GYPP was associated with superiority in NUE and most studied traits. In general, T × T crosses had favorable (higher) values for GYPP and NUE traits than S × S and T × S crosses under low-N stress. Studied genotypes were classified into four groups, based on NUE, GYPP and tolerance to low-N. The parents L26 and L27, the F1's L26 × L27 and L26 × Gem7 and the F2's L25 × L26 and L27 × Gz168 occupied the first group in all classifications; they are N-efficient and high-yielding at low and high N, tolerant to low-N and responsive at high-N.